1. Field of the Invention
The present invention relates to a thermostat malfunction detecting system of an engine cooling system for detecting whether a thermostat for controlling the temperature of coolant of an engine is in malfunction or not.
2. Related Art
Generally, a thermostat which opens/closes in correspondence to the temperature of a coolant (cooling water) is provided in a coolant circulating path for circulating the coolant between a water jacket within an engine and a radiator in the water-cooled type engine. It is closed from the start of the engine until when the warm-up operation is completed to halt the circulation of the coolant to raise the temperature of the coolant quickly to the required temperature range and to improve the fuel consumption and to reduce noxious exhaust emission. The thermostat automatically opens when the temperature of the coolant on the engine side exceeds the required temperature range to circulate the low temperature coolant on the radiator side to the engine side to lower or maintain the temperature of the coolant on the engine side to the required temperature range.
As modes of malfunction of the thermostat, there are an open-malfunction during which the thermostat is kept opened and a closure-malfunction during which it is kept closed. When the open-malfunction occurs, the cold coolant within the radiator is circulated to the engine from the beginning of start even during the cold start time during which the engine is started while it is cold, so that the temperature of the coolant on the engine side is hampered from rising after the start, thus retarding the warm-up of the engine and increasing the fuel consumption and noxious exhaust emission. When the closure-malfunction occurs, the cold coolant on the radiator side is not circulated even when the temperature of the coolant on the engine side exceeds the required temperature range, so that there is a possibility that the temperature of the coolant on the engine side keeps rising, causing an over-heat of the engine in the end.
Thus, there has been a possibility that even when the thermostat has the open-malfunction, a driver continues to drive a vehicle without knowing it for a long period of time and continues to drive the vehicle until engine overheats when it has the closure-malfunction.
It is noted that there has been a technology of providing coolant temperature sensors at the inlet and outlet of the radiator, respectively, to evaluate the heat radiating performance of the radiator based on the temperature of coolant at the inlet and outlet of the radiator to detect the deterioration of the radiator as disclosed in Japanese Patent Application Laid-Open No. Hei. 4-19329. However, because the thermostat opens/closes automatically in correspondence to the temperature of the coolant on the engine side, the malfunction of the thermostat cannot be detected even if the coolant temperature on the radiator side which is not related to the opening/closing operation of the thermostat is detected at the two spots as disclosed. Still more, the cost becomes high because two temperature sensors have to be provided anew on the radiator side.